Code 25 (TBI Federal) - Intake Air Temperature Sensor, High Temperature Indicated: Notes

Intake Air Temperature (IAT) sensor is a thermistor in series with a fixed resistor in ECM. ECM applies and monitors 5 volts to sensor. ECM converts voltage into a temperature reading. When outside air temperature is cold, sensor resistance is high. When outside air temperature is warm, sensor resistance is low. Therefore, when air temperature is cold, ECM receives a high voltage input and when air temperature is warm, ECM receives a low voltage input. Code 25 will set when voltage input at ECM indicates air temperature greater than 284°F (140°C) for at least 5 seconds.

1. This test simulates Code 23. If ECM stores Code 23, ECM and its wiring are okay, and IAT sensor is faulty. If Code 25 resets, IAT sensor is okay, and wiring to ECM or ECM is faulty.